In late March 2019 a study was released that caused exercise physiology textbooks to be tossed in the garbage. This new study examined muscle fibers in elite female athletes and found unexpected results. There are three basic types of muscle fibers in humans: slow-twitch, also known as type-1 muscle fibers or endurance fibers; fast-twitch-2A fibers, which are considered intermediate muscle fibers showing some characteristics of both slow-twitch and fast-twitch muscle fibers; and fast-twitch type-2X fibers, which are usually the muscle fibers that impart the greatest degree of muscular size and strength. For years, male bodybuilders were assumed to have a preponderance of type-2X muscle fibers, which would explain their great degree of muscular size. However, when bodybuilders' muscle fibers were examined under the microscope, it turned out that the bodybuilders showed muscular hypertrophy in primarily the type 2A muscle fibers. This made sense in a way, since most bodybuilders routinely trained with higher repetitions, such as 8 to 12 reps, and this rep range would most involve the type2A fibers. In contrast, to affect the fast-twitch type 2-X fibers would require using heavier weight and lower reps, a range of about 4 to 6 per set.
In regard to women, it was long thought that when women lifted weights the muscle fibers most affected would be the type-1 slow-twitch muscle fibers. This would explain why muscular size was limited in women no matter how hard or how much they trained. Of course, women's smaller bone structure compared to men also played a role in limiting female muscle mass, as did the lower production of testosterone in women.[/pullquote] Even female bodybuilding competitors who used vast amounts of anabolic steroids, which are synthetic versions of testosterone, never duplicate the muscle mass shown by their male counterparts, although they look extremely muscular.[/pullquote] Even female bodybuilding competitors who used vast amounts of anabolic steroids, which are synthetic versions of testosterone, never duplicate the muscle mass shown by their male counterparts, although they look extremely muscular. Again, this was thought to be due to the muscle size limitations induced by the female preponderance of type-1 muscle fibers. But with the publication of a new study that took a closer look at the muscle fibers of elite female athletes, including female Olympic weightlifters, the notion that type-1 fibers predominate in women turned out to be wrong.
What the study involved was an analysis of muscle biopsies or small bits of muscle tissue obtained from the thighs of 6 Olympic class female athletes and 9 national-level female athletes, which were compared to male athletes competing in the 2017 World Weightlifting Championship held in Anaheim, California. The results of viewing these elite female weightlifters muscle fibers showed that they had the highest number of fast-twitch fibers of any athletes previously observed. Two of the women showed that they had 85 percent fast-twitch . . .